1,3-dioxane derivatives having axial fluorine substitution

ABSTRACT

1,3-Dioxane compounds of the formula I 
     
         R.sup.1 --(A.sup.1 --Z.sup.1).sub.m --W--(Z.sup.2 --A.sup.2).sub.n 
    
      --R 2 (I) 
     in which 
     W is ##STR1##  and R 1 , R 2 , A 1 , A 2 , Z 1 , Z 2 , m, n, ##STR2##  n 1 , n 2 , n 3 , n 4 , n 5 , n 6 , Z 3  and Z 4  are as defined herein, 
     are suitable as components of liquid-crystalline media.

The invention relates to 1,3-dioxane derivatives having axial fluorinesubstitution, of the general formula I

    R.sup.1 --(A.sup.1 --Z.sup.1).sub.m --W--(Z.sup.2 --A.sup.2).sub.n --R.sup.2(I)

in which

W is ##STR3## are each, independently of one another, ##STR4## n₁, n₂and n₃ are each, independently of one another, 0 or 1,

where one of the groups ##STR5## must be ##STR6## and another of thesegroups must simultaneously be ##STR7## are each, independently of oneanother, ##STR8## n₄, n₅ and n₆ are each, independently of one another,0 or 1,

where one of the groups ##STR9## must be ##STR10## R¹ and R² are each,independently of one another, an alkyl or alkenyl radical having 1 to 12carbon atoms which is unsubstituted, mono-substituted by CN or CF₃ or atleast mono-substituted by halogen, (e.g., up to perhalosubstituted)where one or more CH₂ groups in these radicals may also be replaced,independently of one another, by --O--, --S--, --CO--, --CO--O--,--O--CO-- or --O--CO--O-- in such a way that hetero atoms are not linkeddirectly to one another,

R² is alternatively F, Cl or CN,

A¹ and A² are each, independently of one another,

a) a trans-1,4-cyclohexylene radical in which, in addition, one or morenon-adjacent CH₂ groups may be replaced by --O-- and/or --S--,

b) a 1,4-cyclohexenylene radical,

c) a 1,4-phenylene radical, in which, in addition, one or two CH groupsmay be replaced by N, or

d) a radical selected front the group consisting of 1,4-bicyclo2.2.2!octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals a), b) and c) may be substituted by CN or F,

Z¹, Z², Z³ and Z⁴ are each, independently of one another,

--CO--O--, --O--CO--, --CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --CH═CH--,--C.tbd.C-- or a single bond, and

m and n are each, independently of one another,

0, 1, 2 or 3,

where n₁ +n₂ +n₃ +m+n=2, 3 or 4, and n₄ +n₅ +n₆ +m+n=1, 2, 3 or 4.

The invention furthermore relates to the use of the compounds of thegeneral formula I as components of liquid-crystalline media and toliquid-crystal and electro-optical display elements which contain theliquid-crystalline media according to the invention.

The compounds of the formula I can be used as components ofliquid-crystalline media, in particular for displays based on theprinciple of the twisted cell, the guest-host effect, the effect ofdeformation of aligned phases (DAP) or ECB (electrically controlledbirefringence) or the effect of dynamic scattering. The substancesemployed hitherto for this purpose all have certain disadvantages, forexample inadequate stability to the action of heat, light or electricfields, or unfavorable elastic and/or dielectric properties.

Compounds which contain a 1- or 4-fluorocyclohexane-1,4-diyl unit aredisclosed, for example, in GB 2,248,059 A and EP 0,107,759 B1, but nocompounds which additionally contain a 1,3-dioxane-2,5-diyl unit aredescribed therein.

Compounds which contain a 5-fluoro-1,3-dioxane-2,5-diyl unit aredisclosed, for example, in

J. Dubois, C. Foures, S. Bory, S. Falcon, M. Gaudry, A. Marquet,Tetrahedron (1991), 47 (6), 1001-1012;

EP 381 531 A2;

T. Ishihara, M. Kuroboshi, K. Yamaguchi, Y. Okada, J. Org. Chem. (1990),55 (10), 3107-3114;

T. Yamazaki, T. Yamamoto, T. Kitazume, J. Org. Chem. (1989), 54 (1),83-91,

but the compounds described therein contain two methyl groups inposition 2 of the 5-fluoro-1,3-dioxane-2,5-diyl unit.

The invention has an object of finding novel, stable, liquid-crystallineor mesogenic compounds which are suitable as components ofliquid-crystalline media, in particular for TFT and STN displays.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

It has now been found that compounds of the formula I are eminentlysuitable as components of liquid-crystalline media. They can be used toobtain stable liquid-crystalline media, particularly suitable for TFT orSTN displays. The novel compounds are distinguished by high thermalstability and have advantageous values for the holding ratio. Thecompounds of the formula I have, in particular, highly negativedielectric anisotropy Δε and are therefore particularly suitable fordisplays based on the effect of deformation of aligned phases. Thecompounds of the formula I according to the invention are furthermoredistinguished by very low optical anisotropy values Δn and favorablephase behavior and good viscoelastic properties.

In addition, the provision of compounds of the formula I very generallyconsiderably broadens the range of liquid-crystalline substances whichare suitable, from various applicational points of view, for thepreparation of liquid-crystalline mixtures.

The compounds of the formula I have a broad range of applications.Depending on the choice of substituents, these compounds can serve asbase materials of which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or to optimize its threshold voltageand/or its viscosity.

The meaning of the formula I includes all isotopes of the chemicalelements bound in the compounds of the formula I.

In the pure state, the compounds of the formula I are colorless and formliquid-crystalline mesophases in a temperature range which is favorablylocated for electro-optical use. They are stable chemically, thermallyand to light.

The invention thus relates to compounds of the formula I and to the useof these compounds as components of liquid-crystalline media. Theinvention furthermore relates to liquid-crystalline media containing atleast one compound of the formula I, and to liquid-crystal displayelements, in particular electro-optical display elements, which containmedia of this type.

Above and below, R¹, R², Z¹, Z², A¹, A², W, m, n, ##STR11## n₁, n₂, n₃,n₄, n₅, n₆, Z³ and Z⁴ are as defined above, unless expressly statedotherwise.

For reasons of simplicity, Cyc^(a) below denotes a 1,4-cyclohexyleneradical, Che denotes a 1,4-cyclo-hexenylene radical, Dio denotes a1,3-dioxane-2,5-diylradical, Dit denotes a dithiane-2,5-diyl radical,Phe^(a) denotes a 1,4-phenylene radical, Pyd denotes a pyridine-2,5-diylradical, Pyr^(a) denotes a pyridine-2,5-diyl radical and Bco denotes abicyclo 2.2.2!-octylene radical, where Cyc^(a) and/or Phe^(a) may beunsubstituted or monosubstituted or polysubstituted by F or CN.

The compounds of the formula I according to the invention include, forexample, compounds containing no ring in the mesogenic groups R¹ --(A¹--Z¹)_(m) -- and --(Z² --A²)_(n) --R², of the subformula II:

    R.sup.1 --W--R.sup.2                                       I 1,

compounds containing one ring in the mesogenic groups R¹ --(A¹ --Z¹)_(m)-- and --(Z² --A²)_(n) --R², of the subformilae I2 to I5:

    R.sup.1 --A.sup.1 --W--R.sup.2                             I 2

    R.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2                   I 3

    R.sup.1 --W--A.sup.2 --R.sup.2                             I 4

    R.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2                   I 5

compounds containing two rings in the mesogenic groups R¹ --(A¹--Z¹)_(m) -- and --(Z² --A²)_(n) --R², of the subformula I6 to I17:

    R.sup.1 --A.sup.1 --A.sup.1 --W--R.sup.2                   I 6

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --W--R.sup.2         I 7

    R.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2         I 8

    R.sup.1 --A.sup.1 Z.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2 I 9

    R.sup.1 --A.sup.1 --W--A.sup.2 --R.sup.2                   I 10

    R.sup.1 --A.sup.1 --Z.sup.1 --W--A.sup.2 --R.sup.2         I 11

    R.sup.1 --A.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2         I 12

    R.sup.1 --A.sup.1 --Z.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2I 13

    R.sup.1 --W--A.sup.2 --A.sup.2 --R.sup.2                   I 14

    R.sup.1 --W--Z.sup.2 --A.sup.2 --A.sup.2 --R.sup.2         I 15

    R.sup.1 --W--A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2         I 16

    R.sup.1 --W--Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 17

and compounds containing three rings in the mesogenic groups R¹ --(A¹--Z¹)_(m) -- and --(Z² --A²)_(n) --R², of the subformulae I18 to I49:

    R.sup.1 --A.sup.1 --A.sup.1 --A.sup.1 --W--R.sup.2         I 18

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --A.sup.1 --W--R.sup.2I 19

    R.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --W--R.sup.2I 20

    R.sup.1 --A.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2I 21

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --W--R.sup.2I 22

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2I 23

    R.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2I 24

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --W--R.sup.2                                              I 25

    R.sup.1 --A.sup.1 --A.sup.1 --W--A.sup.2 --R.sup.2         I 26

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --W--A.sup.2 --R.sup.2I 27

    R.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --W--A.sup.2 --R.sup.2I 28

    R.sup.1 --A.sup.1 --A.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2I 29

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --W--A.sup.2 --R.sup.2I 30

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2I 31

    R.sup.1 --A.sup.1 --A.sup.1 --Z.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2I 32

    R.sup.1 --A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --W--Z.sup.2 --A.sup.2 --R.sup.2                                                 I 33

    R.sup.1 --A.sup.1 --W--A.sup.2 --A.sup.2 --R.sup.2         I 34

    R.sup.1 --A.sup.1 --Z.sup.1 --W--A.sup.2 --A.sup.2 --R.sup.2I 35

    R.sup.1 --A.sup.1 --W--Z.sup.2 --A.sup.2 --A.sup.2 --R.sup.2I 36

    R.sup.1 --A.sup.1 --W--A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 37

    R.sup.1 --A.sup.1 --Z.sup.1 --W--Z.sup.2 --A.sup.2 --A.sup.2 --R.sup.2I 38

    R.sup.1 --A.sup.1 --Z.sup.1 --W--A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 39

    R.sup.1 --A.sup.1 --W--Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 40

    R.sup.1 --A.sup.1 --Z.sup.1 --W--Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2                                                 I 41

    R.sup.1 --W--A.sup.2 --A.sup.2 --A.sup.2 --R.sup.2         I 42

    R.sup.1 --W--Z.sup.2 --A.sup.2 --A.sup.2 --A.sup.2 --R.sup.2I 43

    R.sup.1 --W--A.sup.2 --Z.sup.2 --A.sup.2 --A.sup.2 --R.sup.2I 44

    R.sup.1 --W--A.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 45

    R.sup.1 --W--Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --A.sup.2 --R.sup.2I 46

    R.sup.1 --W--Z.sup.2 --A.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 47

    R.sup.1 --W--A.sup.2 --Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2I 48

    R.sup.1 --W--Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --Z.sup.2 --A.sup.2 --R.sup.2                                                 I 49.

Of these, particular preference is given to the subformulae I1, I2, I3,I4, I5, I6, I7, I10, I14 and I16.

The preferred compounds of the subformula I2 include those of thesubformulae I2a and I2b:

    R.sup.1 --Phe.sup.a --W--R.sup.2                           I 2a

    R.sup.1 --Cyc.sup.a --W--R.sup.2                           I 2b.

The preferred compounds of the subformula I3 include those of thesubformulae I3a to I3c:

    R.sup.1 --Phe.sup.a --Z.sup.1 --W--R.sup.2                 I 3a

    R.sup.1 --Cyc.sup.a --Z.sup.1 --W--R.sup.2                 I 3b

    R.sup.1 --A.sup.1 --CH.sub.2 CH.sub.2 --W--R.sup.2         I 3c.

The preferred compounds of the subformula I4 include those of thesubformulae I4a and I4b:

    R.sup.1 --W--Phe.sup.a --R.sup.2                           I 4a

    R.sup.1 --W--Cyc.sup.a --R.sup.2                           I 4b.

The preferred compounds of the subformula I5 include those of thesubformulae I5a to I5c:

    R.sup.1 --W--Z.sup.2 --Phe.sup.a --R.sup.2                 I 5a

    R.sup.1 --W--Z.sup.2 --Cyc.sup.a --R.sup.2                 I 5b

    R.sup.1 --W--CH.sub.2 CH.sub.2 --A.sup.2 --R.sup.2         I 5c.

The preferred compounds of the subformulae I6 include those of thesubformulae I6a to I6g:

    R.sup.1 --Cyc.sup.a --Cyc.sup.a --W--R.sup.2               I 6a

    R.sup.1 --Cyc.sup.a --Phe.sup.a --W--R.sup.2               I 6b

    R.sup.1 --Phe.sup.a --Phe.sup.a --W--R.sup.2               I 6c

    R.sup.1 --Pyd--Phe.sup.a --W--R.sup.2                      I 6d

    R.sup.1 --Phe.sup.a --Cyc.sup.a --W--R.sup.2               I 6e

    R.sup.1 --Dio--Phe.sup.a --W--R.sup.2                      I 6f

    R.sup.1 --Pyr.sup.a --Phe.sup.a --W--R.sup.2               I 6g.

Of these, particular preference is given to those of the subformulaeI6a, I6b, I6c and I6e.

The preferred compounds of the subformula I7 include those of thesubformulae I7a to I7h:

    R.sup.1 --Cyc.sup.a --Z.sup.1 --Cyc.sup.a --W--R.sup.2     I 7a

    R.sup.1 --A.sup.1 --CH.sub.2 CH.sub.2 --A.sup.1 --W--R.sup.2I 7b

    R.sup.1 --Cyc.sup.a --Z.sup.1 --Phe.sup.a --W--R.sup.2     I 7c

    R.sup.1 --A.sup.1 --OCO--Phe.sup.a --W--R.sup.2            I 7d

    R.sup.1 --Phe.sup.a --Z.sup.1 --Phe.sup.a --W--R.sup.2     I 7e

    R.sup.1 --Pyr.sup.a --Z.sup.1 --A.sup.1 --W--R.sup.2       I 7f

    R.sup.1 --Pyd--Z.sup.1 --A.sup.1 --W--R.sup.2              I 7g

    R.sup.1 --Dio--Z.sup.1 --A.sup.1 --W--R.sup.2              I 7h.

Of these, particular preference is given to those of the subformulaeI7a, I7b, I7c and I7e.

The preferred compounds of the subformula I10 include those of thesubformulae I10a to I10g:

    R.sup.1 --Cyc.sup.a --W--Cyc.sup.a --R.sup.2               I 10a

    R.sup.1 --Cyc.sup.a --W--Phe.sup.a --R.sup.2               I 10b

    R.sup.1 --Phe.sup.a --W--Phe.sup.a --R.sup.2               I 10c

    R.sup.1 --Dio--W--A.sup.2 --R.sup.2                        I 10d

    R.sup.1 --A.sup.1 --W--Dio--R.sup.2                        I 10e

    R.sup.1 --Phe.sup.a --W--Cyc.sup.a --R.sup.2               I 10f

    R.sup.1 --A.sup.1 --W--Che--R.sup.2                        I 10g.

Of these, particular preference is given to those of the subformulaeI10a, I10b, I10c and I10f.

The preferred compounds of the subformula I14 include those of thesubformulae I14a to I14g:

    R.sup.1 --W--Cyc.sup.a --Cyc.sup.a --R.sup.2               I 14a

    R.sup.1 --W--Phe.sup.a --Cyc.sup.a --R.sup.2               I 14b

    R.sup.1 --W--Phe.sup.a --Phe.sup.a --R.sup.2               I 14c

    R.sup.1 --W--Phe.sup.a --Pyd--R.sup.2                      I 14d

    R.sup.1 --W--Cyc.sup.a --Phe.sup.a --R.sup.2               I 14e

    R.sup.1 --W--Phe.sup.a --Dio--R.sup.2                      I 14f

    R.sup.1 --W--Phe.sup.a --Pyr.sup.a --R.sup.2               I 14g.

Of these, particular preference is given to those of the subformulaeI14a, I14b, I14c and I14e.

The preferred compounds of the subformula I16 include those of thesubformulae I16a to I16h:

    R.sup.1 --W--Cyc.sup.a --Z.sup.2 --Cyc.sup.a --R.sup.2     I 16a

    R.sup.1 --W--A.sup.2 --CH.sub.2 CH.sub.2 --A.sup.2 --R.sup.2I 16b

    R.sup.1 --W--Phe.sup.a --Z.sup.2 --Cyc.sup.a --R.sup.2     I 16c

    R.sup.1 --W--Phe.sup.a --COO--A.sup.2 --R.sup.2            I 16d

    R.sup.1 --W--Phe.sup.a --Z.sup.2 --Phe.sup.a --R.sup.2     I 16e

    R.sup.1 --W--A.sup.2 --Z.sup.2 --Pyr.sup.a --R.sup.2       I 16f

    R.sup.1 --W--A.sup.2 --Z.sup.2 --Pyd--R.sup.2              I 16g

    R.sup.1 --W--A.sup.2 --Z.sup.2 --Dio--R.sup.2              I 16h.

Of these, particular preference is given to those of the subformulaeI16a, I16b, I16c and I16e.

In the compounds of the formulae above and below, R¹ and R² arepreferably unsubstituted, straight-chain alkyl, alkenyl, oxalkyl oroxalkenyl having 1 to 12 carbon atoms; R¹ and R² are particularlypreferably unsubstituted, straight-chain alkyl having 1 to 7 carbonatoms or unsubstituted, straight-chain alkenyl having 2 to 10 carbonatoms. The alkenyl radical is preferably 1E-alkenyl, 3E-alkenyl or4-alkenyl and particularly preferably 1E- or 3E-alkenyl. R² issecondarily preferably F, Cl, OCF₃, OCHF₂, CF₃, CHF₂, OCHFCF₃, OCHFCHF₂,OCH₂ CF₃, OC₂ F₅, OC₃ F₇, OCF═CHF, OCF₂ CHFCF₃, in particular F, OCF₃,OCHF₂, OCHFCF₃ or OCHFCHF₂.

A¹ and A² are preferably, independently of one another, Phe^(a),Cyc^(a), Che, Pyd or Pyr^(a), particularly preferably Phe^(a), Cyc^(a)or Che, especially preferably Phe^(a) or Cyc^(a).

A¹ and A² are preferably, independently of one another, ##STR12## wherethe rings can also occur in inverted form.

If the ring A¹ is present more than once, these rings can have identicalor different meanings. The same also applies to the ring A², and to thebridges Z¹ and Z².

Z¹, Z², Z³ and Z⁴ are preferably, independently of one another, CH₂ CH₂or a single bond, particularly preferably a single bond.

m and n are preferably, independently of one another, 0, 1 or 2,particularly preferably 0 or 1.

The sum n₁ +n₂ +n₃ +m+n is preferably 2 or 3, particularly preferably 2.

The sum n₄ +n₅ +n₆ +m+n is preferably 1, 2 or 3, particularly preferably2 or 3, especially preferably 2.

The formulae 1 to 17 ^(show) particularly preferred meanings of thestructural unit W ##STR13## L¹, L² and L³ are each, independently of oneanother, H or F. One of the radicals L^(1*), L^(2*) and L^(3*) is F, andthe other radicals L^(1*), L^(2*) and L^(3*) are each, independently ofone another, H or F. If only two of the radicals L^(1*), L^(2*) andL^(3*) are present in a formula, i.e. L^(1*) and L^(2*) or L^(1*) andL^(3*) or L^(2*) and L^(3*), one of these two radicals is F and theother is H or F.

Of these structural units W, those of the formula 1 to 10 areparticularly preferred.

In all compounds of the formula I, the fluorine atoms in the structuralunits W are in the axial position in the fluorocyclohexane or5-fluoro-1,3-dioxane units. The other substituents are in thetrans-arrangement to one another. This connection is illustrated by wayof example with reference to the following preferred compounds accordingto the invention: ##STR14## in which one of the radicals L^(1*) andL^(2*) is F and the other of these radicals is H or F, and y is 1 or 2,and R¹ and R² are as defined above.

If R¹ and R² are an alkyl and/or an alkoxy radical, this can bestraight-chain or branched. It is preferably straight-chain, has 2, 3,4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl,butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxyor heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl,methoxy, octoxy, nonoxy, decoxy or undecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl),2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl,2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl,or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R¹ and R² are an alkenyl radical, this can be straight-chain orbranched. It is preferably straight-chain and has 2 to 10 carbon atoms.Accordingly, it is in particular vinyl, prop-1- or 2-enyl, but-1-, -2-or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or-5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-,-5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, ordec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

If R¹ and R² are an alkenyl radical in which one CH₂ group has beenreplaced by --O--, this can be straight-chain or branched. It ispreferably straight-chain and has 2 to 10 carbon atoms. Accordingly, itis in particular vinyloxy, prop-1- or -2-enyloxy, but-1-, -2- or-3-enyloxy, pent-1-, -2-, -3- or -4-enyloxy, hex-1-, -2-, -3-, -4- or-5-enyloxy, hept-1-, -2-, -3-, -4-, -5- or -6-enyloxy, oct-1-, -2-, -3-,-4-, -5-, -6- or -7-enyloxy, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or-8-enyloxy or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyloxy or2-oxabut-3-enyl (vinyloxymethyl), 2-oxapent-3- or -4-enyl or3-oxapent-4-enyl, 2-oxahex-3-, -4- or -5-enyl, 3-oxahex-4- or -5-enyl or4-oxahex-5-enyl, 2-oxahept-3-, -4-, -5- or -6-enyl, 3-oxahept-4-, -5- or-6-enyl, 4-oxahept-5- or -6-enyl or 5-oxahept-6-enyl, 2-oxaoct-3-, -4-,-5-, -6- or -7-enyl, 3-oxaoct-4-, -5-, -6- or -7-enyl, 4-oxaoct-5-, -6-or -7-enyl, 5-oxaoct-6- or -7-enyl or 6-oxaoct-7-enyl, 2-oxanon-3-, -4-,-5-, -6-, -7- or -8-enyl, 3-oxanon-4-, -5-, -6-, -7- or -8-enyl,4-oxanon-5-, -6-, -7- or -8-enyl, 5-oxanon-6-, -7- or -8-enyl,6-oxanon-7- or -8-enyl or 7-oxanon-8-enyl or 2-oxadec-3-, -4-, -5-, -6-,-7-, -8- or -9-enyl, 3-oxadec-4-, -5-, -6-, -7-, -8- or -9-enyl,4-oxadec-5-, -6-, -7-, -8- or -9-enyl, 5-oxadec-6-, -7-, -8- or -9-enyl,6-oxadec-7-, -8- or -9-enyl, 7-oxadec-8- or -9-enyl or 8-oxadec-9-enyl,2-oxaundec-3-, -4-, -5-, -6-, -7-, -8-, -9- or -10-enyl, 3-oxaundec-4-,-5-, -6-, -7-, -8-, -9- or -10-enyl, 4-oxaundec-5-, -6-, -7-, -8-, -9-or -10-enyl, 5-oxaundec-6-, -7-, -8-, -9- or -10-enyl, 6-oxaundec-7-,-8-, -9- or -10-enyl, 7-oxaundec-8-, -9-or -10-enyl, 8-oxaundec-9- or-10-enyl or 9-oxaundec-10-enyl.

If R¹ and R² are an alkyl radical in which one CH₂ group has beenreplaced by --O-- and one has been replaced by --CO--, these arepreferably adjacent. They thus contain an acyloxy group --CO--O--or anoxycarbonyl group --O--CO--. These are preferably straight-chain andhave 2 to 6 carbon atoms. Accordingly, they are in particular acetyloxy,propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl,propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl,2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl,3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl, 4-(methoxycarbonyl)butyl.

If R¹ and R² are an alkyl or alkenyl radical which is monosubstituted byCN or CF₃, this radical is preferably straight-chain, and thesubstitution by CN or CF₃ is in the ω-position.

If R¹ and R² are an alkyl or alkenyl radical which is at leastmonosubstituted by halogen, this radical is preferably straight-chain,and halogen is preferably F or Cl. In the case of multiple substitution,halogen is preferably F. The resultant radicals also includeperfluorinated radicals. In the case of monosubstitution, the fluorineor chlorine substituent can be in any desired position, but ispreferably in the ω-position.

Compounds of the formula I having branched wing groups R¹ and R² mayoccasionally be of importance owing to better solubility in theconventional liquid-crystalline base materials, but in particular aschiral dopants if they are optically active. Smectic compounds of thistype are suitable as components of ferro-electric materials.

Compounds of the formula I having S_(A) phases are suitable, forexample, for thermally addressed displays.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched radicals R¹ and R² are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy, 1-methylheptoxy.

The formula I also covers the raceLTnates of these canpounds and theoptical antipodes, and mixtures thereof.

Of these compounds of the formula I and of the subformulae, preferenceis given to those in which at least one of the radicals present thereinhas one of the preferred meanings indicated.

Some very particularly preferred subgeneric groups of compounds of theformula I according to the invention are those of the subformulae Ia1 toIh6: ##STR15## L¹, L², L³, L^(a), L^(b), L^(c) and L^(d) are each,independently of one another, H or F. One of the radicals L^(1*), L^(2*)and L^(3*) is F, and the other radicals L^(1*), L^(2*) and L^(3*) areeach, independently of one another, H or F. If only two of the radicalsL^(1*), L^(2*) and L^(3*) are present in a formula, i.e. L^(1*) andL^(2*) or L^(1*) and L^(3*) or L^(2*) and L^(3*), one of these tworadicals is F and the other is H or F.

Of the compounds of the formulae Ia1 to Ih6, preference is given tothose of the formulae Ia1 to Ia3, Ib1 to Ib6, Id1 and Id2. Particularlypreferred compounds of the formulae Ia1 to Ia3, Ib1 to Ib6, Id1 and Id2are those in which R¹ and R² are each, independently of one another, analkyl radical having 1 to 12 carbon atoms, preferably a straight-chain,unsubstituted alkyl radical having 1 to 7 carbon atoms, or an alkenylradical having 2 to 12 carbon atoms, preferably a straight-chain,unsubstituted alkenyl radical having 2 to 10 carbon atoms. Of thesealkenyl radicals, particular preference is given to the 1E-alkenyl and3E-alkenyl radicals.

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works, such asHouben-Weyl, Methoden der Organischen Chemie, Georg-Thieme-Verlag,Stuttgart), to be precise under reaction conditions which are known andsuitable for said reactions.

Use can also be made here of variants which are known per se, but arenot mentioned here in greater detail.

The starting materials are either known or can be prepared by knownmethods. If desired, they can also be formed in situ by not isolatingthem from the reaction mixture, instead immediately converting them intothe compounds of the formula I.

The compounds according to the invention can be prepared, for example,in accordance with the following reaction schemes: ##STR16## R¹ --(A¹--Z¹)_(m) -- in the reaction described in this scheme is preferablyalkyl, aryl, 4-alkoxycyclohexyl or 4-arylcyclohexyl. ##STR17## --(Z²--A²)_(n) --R² in the reaction described in this scheme is preferablyalkyl, alkenyl or aryl. Scheme 5 ##STR18##

One of the radicals L^(1*) and L^(2*) is F, and the other is H or F.##STR19##

One of the radicals L^(1*) and L^(2*) is F, and the other is H or F.##STR20##

One of the radicals L^(1*) and L^(2*) is F, and the other is H or F.##STR21##

By reacting ##STR22## with NaH/THF and Selectfluor/DMF, it is alsopossible to prepare the compound OHC--CHF--(CH₂ OCH₂ C₆ H₅)₂. ##STR23##

One of the radicals L^(1*), L^(2*) and L^(3*) is F, and the otherradicals L^(1*), L^(2*) and L^(3*) are each, independently of oneanother, H or F.

Preferred compounds of the formula I are prepared as follows: ##STR24##

The liquid-crystalline media according to the invention preferablycomprise from 2 to 40, in particular from 4 to 30, components as furtherconstituents besides one or more compounds according to the invention.These media very particularly preferably comprise from 7 to 25components besides one or more compounds according to the invention.These further constituents are preferably selected from nematic ornematogenic (monotropic or isotropic) substances, in particularsubstances from the classes of the azoxybenzenes, benzylideneanilines,biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl orcyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexylesters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters ofcyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoicacid, of cyclohexanecarboxylic acid and ofcyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohaxenes,1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- orcyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- orcyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1,2-diphenylethanes, 1,2-di-cyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-bi-phenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:

    R'--A--E--R"                                               1

    R'--A--COO--E--R"                                          2

    R'--A--OOC--E--R"                                          3

    R'--A--CH.sub.2 CH.sub.2 --E--R"                           4

    R'--A--C.tbd.C--E--R"                                      5

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are in each case, independently of one another, a bivalentradical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-,-Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images,where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc istrans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr is pyridine-2,5-diylor pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl and G is2-(trans-1,4-cyclohexyl)ethyl, pyridine-2,5-diyl, pyridine-2,5-diyl or1,3-dioxane-2,5-diyl.

One of the radicals A and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably comprise one or more components selected from the compoundsof the formulae 1, 2, 3, 4 and 5 in which A and E are selected from thegroup consisting of Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals A and E is selected from the groupconsisting of Cyc, Phe and Pyr and the other radical is selected fromthe group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and-G-Cyc-, and optionally one or more components selected from thecompounds of the formulae 1, 2, 3, 4 and 5 in which the radicals A and Eare selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe-and -G-Cyc-.

In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and5, R' and R" are in each case, independently of one another, alkyl,alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8carbon atoms. This smaller sub-group is called group A below, and thecompounds are labelled with the sub-formulae 1a, 2a, 3a, 4a and 5a. Inmost of these compounds, R' and R" are different from one another, oneof these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4and 5 which is known as group B, R" is --F, --Cl, --NCS or --(O)_(i)CH₃₋(k+l) F_(k) Cl_(l), where i is 0 or 1, and k+l is 1, 2 or 3; thecompounds in which R" has this meaning are labelled with thesub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given tothose compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which R" is--F, --Cl, --NCS, --CF₃, --OCHF₂ or --OCF₃.

In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, R' is asdefined for the compounds of the sub-formulae 1a-5a and is preferablyalkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller sub-group of the compounds of the formulae 1, 2, 3,4 and 5, R" is --CN; this sub-group is known as group C below, and thecompounds of this sub-group are correspondingly described bysub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae1c, 2c, 3c, 4c and 5c, R' is as defined for the compounds of thesub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.

In addition to the preferred compounds of groups A, B and C, othercompounds of the formulae 1, 2, 3, 4 and 5 having other variants of theproposed substituents are also customary. All these substances can beobtained by methods which are known from the literature or analogouslythereto.

Besides compounds of the formula I according to the invention, the mediaaccording to the invention preferably comprise one or more compoundsselected from group A and/or group B and/or group C. The proportions byweight of the compounds from these groups in the media according to theinvention are preferably

Group A: from 0 to 90%, preferably from 10 to 90%, in particular from 30to 90%

Group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10to 65%

Group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5to 50%,

the sum of the proportions by weight of the group A and/or B and/or Ccompounds present in the particular media according to the inventionpreferably being from 5 to 90% and in particular from 10 to 90%.

The media according to the invention preferably comprise from 1 to 40%,particularly preferably from 5 to 30%, of compounds according to theinvention. Further preferred media are those which comprise more than40%, in particular from 45 to 90%, of compounds according to theinvention. The media preferably comprise three, four or five compoundsaccording to the invention.

The media according to the invention are prepared in a manner which iscustomary per se. In general, the components are dissolved in oneanother, expediently at elevated temperature. By means of suitableadditives, the liquid-crystalline phases can be modified in accordancewith the invention in a manner such that they can be used in all typesof liquid-crystal display elements which have hitherto been disclosed.Additives of this type are known to those skilled in the art and aredescribed in detail in the literature (H. Kelker/R. Hatz, Handbook ofLiquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroicdyes can be added for the production of coloured guest-host systems, orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the alignment of the nematic phases.

The entire disclosure of all applications, patents and publications,cited above and below, and of corresponding German application No. 19723 277.9, filed Jun. 4, 1997 is hereby incorporated by reference.

EXAMPLES

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by acronyms, thetransformation into chemical formulae taking place as in Tables A and Bbelow. All the radicals C_(n) H_(2n+1) and C_(m) H_(2m+1) arestraight-chain alkyl radicals containing n or m carbon atomsrespectively. The coding in Table B is self-evident. In Table A, onlythe acronym for the parent structure is given. In individual cases, theacronym for the parent structure is followed, separated by a hyphen, bya code for the substituents R¹, R², L¹ and L² :

    ______________________________________    Code for R.sup.1,    R.sup.2, L.sup.1, L.sup.2             R.sup.1          R.sup.2    L.sup.1                                             L.sup.2    ______________________________________    nm       C.sub.n H.sub.2n+1                              C.sub.m H.sub.2m+1                                         H   H    nOm      C.sub.n H.sub.2n+1                              OC.sub.m H.sub.2m+1                                         H   H    nO.m     OC.sub.n H.sub.2n+1                              C.sub.m H.sub.2m+1                                         H   H    n        C.sub.n H.sub.2n+1                              CN         H   H    nN.F     C.sub.n H.sub.2n+1                              CN         H   F    nF       C.sub.n H.sub.2n+1                              F          H   H    nOF      OC.sub.n H.sub.2n+1                              F          H   H    nCl      C.sub.n H.sub.2n+1                              Cl         H   H    nF.F     C.sub.n H.sub.2n+1                              F          H   F    nF.F.F   C.sub.n H.sub.2n+1                              F          F   F    nCF.sub.3             C.sub.n H.sub.2n+1                              CF.sub.3   H   H    nOCF.sub.3             C.sub.n H.sub.2n+1                              OCF.sub.3  H   H    nOCF.sub.2             C.sub.n H.sub.2n+1                              OCHF.sub.2 H   H    nS       C.sub.n H.sub.2n+1                              NCS        H   H    rVsN     C.sub.r H.sub.2r+1 --CH═CH--C.sub.s H.sub.2S --                              CN         H   H    rEsN     C.sub.r H.sub.2r+1 --O--C.sub.s H.sub.2s --                              CN         H   H    nAm      C.sub.n H.sub.2n+1                              COOC.sub.m H.sub.2m+1                                         H   H    ______________________________________

                                      TABLE A    __________________________________________________________________________     ##STR25##                                  2 #STR26##    PYP                           PYRP    3 #STR27##                                  4 #STR28##    BCH                           CBC    5 #STR29##                                  6 #STR30##    CCH                           CCP    7 #STR31##                                  8 #STR32##    CP                            CPTP    9 #STR33##    CEPTP     ##STR34##                                  1 #STR35##    D                             ECCP    2 #STR36##                                  3 #STR37##    CECP                          EPCH    4 #STR38##                                  5 #STR39##    HP                            ME    6 #STR40##                                  7 #STR41##    PCH                           PDX    8 #STR42##                                  9 #STR43##    PTP                           BECH    0 #STR44##                                  1 #STR45##    EBCH                          CPC    2 #STR46##                                  3 #STR47##    DDP                           DDCP    4 #STR48##                                  5 #STR49##    DD                            DDD    __________________________________________________________________________

                                      TABLE B    __________________________________________________________________________     ##STR50##                                   7 #STR51##    T15                            K3n    8 #STR52##                                   9 #STR53##    M3n                            BCH-n.Fm    0 #STR54##    Inm    1 #STR55##    C-nm     ##STR56##    2                                   3 #STR57##    C15                            CB15    4 #STR58##    CBC-nmF    5 #STR59##    CH-nm    6 #STR60##    CCPC-nm    7 #STR61##    HD-nm    8 #STR62##    HH-nm     ##STR63##    9                                   0 #STR64##    NCB-nm                         CCN-nm    1 #STR65##                                   2 #STR66##    OS-nm                          CHE    3 #STR67##    ECBC-nm     ##STR68##    4                                   5 #STR69##    ECCH-nm                        CCH-n1EM    6 #STR70##                                   7 #STR71##    T-nFm                          ECCH-nm    8 #STR72##                                   9 #STR73##    CCH-n1EM                       T-nFN    0 #STR74##                                   1 #STR75##    CCP-nF.F.F                     DCU-n-X    2 #STR76##                                   3 #STR77##    DCU-n-X                        DD-n-Vm    __________________________________________________________________________

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, per cent data are per centby weight. All temperatures are given in degrees Celsius. b.p. denotesboiling point, m.p.=melting point, cl.p.=clearing point. Furthermore,C=crystalline state, N=nematic phase, S=smectic phase and I=isotropicphase. The numbers between these symbols indicate the conversiontemperature in degrees Celsius. Δn denotes optical anisotropy (589 nm,20° C.), and the viscosity (mm² /sec) was determined at 20° C.

"Conventional work-up" means that water is added if necessary, themixture is extracted with dichloromethane, diethyl ether, n-pentane ortoluene, the organic phase is separated off, dried and evaporated, andthe product is purified by distillation under reduced pressure orcrystallization and/or chromatography. The following abbreviations areused:

    ______________________________________    NaH         sodium hydride    TsOH        p-toluenesulphonic acid (also                abbreviated to pTsOH)    BnBr        benzyl bromide    Pd/C        palladium on activated charcoal    CH.sub.3 CN acetonitrile    Et.sub.2 O  diethyl ether    tBu         tert-butyl    ClSi (CH.sub.3).sub.3                chlorotrimethylsilane    THF         tetrahydrofuran    LiAlH.sub.4 lithium aluminium hydride    NEt.sub.3   triethylamine    DMF         N,N-dimethylformamide    Me.sub.3 SiOTf                trimethylsilyl                trifluoromethanesulphonate (also                abbreviated to TMSOTf)    Selectfluor N-fluoro-N-chloromethyltriethylenediamine                bis(tetrafluoroborate)    Ph.sub.3 PCHOCH.sub.3                methoxymethylenetriphenylphosphane    ______________________________________

Example 1

Step 1 ##STR78##

A mixture of 150 mmol of NaH and 300 ml of THF is cooled to 0° C. underinert gas, and a solution of 110 mmol of diethyl propylmalonate (1) in100 ml of THF is added dropwise. After the mixture has been stirred for5 hours (2 h at 0° C., 1 h at room temperature and 2 h at 40° C.), asuspension of 129 mmol of Selectfluor in 200 ml of acetonitrile is addedat from 0° C. to 5° C., and stirring is continued for a further 12 h.The mixture is subsequently subjected to conventional work-up.Chromatography and distillation under reduced pressure give 2.

Step 2 ##STR79##

A solution of 64 mmol of 2 in 20 ml of THF is added dropwise at -30° C.under inert gas to a mixture of 105 mmol of LiAlH₄, 25 ml of toluene and90 ml of THF. The mixture is stirred for a further 20 minutes at 30° C.and for 1.5 hours at 20° C. and then hydrolysed using a solution of 101mmol of sodium carbonate decahydrate in 12 ml of water. The mixture issubsequently subjected to conventional work-up. Chromatography gives 3.

Step 3 ##STR80##

80 mmol of chlorotrimethylsilane are added dropwise under inert gas to amixture of 29 mmol of 3, 160 mmol of triethylamine and 50 ml ofN,N-dimethylformamide at such a rate that the temperature does not riseabove 30° C. The mixture is stirred at room temperature for a further 2hours, 100 ml of n-pentane are added, and the mixture is stirred for afurther 5 minutes and subjected to a conventional work-up. Distillationunder reduced pressure gives 4.

Step 4 ##STR81##

25 mmol of trans-4-n-propylcyclohexane aldehyde in 20 ml of CH₂ Cl₂ areadded dropwise at -70° C. under inert gas to a mixture of 20 mmol of 4,80 ml of CH₂ Cl₂ and 3 mmol of trimethylsilyltrifluoromethanesulphonate. After the mixture has been stirred at -70°C. for 2 hours, 30 mmol of pyridine are added dropwise, the mixture isslowly warmed to room temperature, 100 ml of saturated NaHCO₃ solutionare added, the mixture is stirred for a further 0.25 h and thensubjected to conventional work-up. Chromatography and recrystallizationfrom hexane give 5; C 112 I; Δε=-4.3; Δn=+0.036.

The following compounds of the formula I

    R.sup.1 --(A.sup.1 --Z.sup.1).sub.m --W--(Z.sup.2 --A.sup.2).sub.n --R.sup.2(I)

are prepared analogously to the above Example 1:

Examples

    __________________________________________________________________________    No.       R.sup.1 --(A.sup.1 --Z.sup.1).sub.m --W--(Z.sup.2 --A.sup.2).sub.n                                                  R.sup.2    __________________________________________________________________________     2 C.sub.2 H.sub.5               1 #STR82##                         C.sub.2 H.sub.5     3 C.sub.2 H.sub.5               1 #STR83##                         n-C.sub.3 H.sub.7     4 n-C.sub.3 H.sub.7               1 #STR84##                         n-C.sub.5 H.sub.11     5 H.sub.3 COC.sub.2 H.sub.4 CH.sub.2               1 #STR85##                         n-C.sub.3 H.sub.7     6 n-C.sub.3 H.sub.7               1 #STR86##                         CH═CH.sub.2     7 n-C.sub.3 H.sub.7               1 #STR87##                         CH═CH--CH.sub.3     8 C.sub.2 H.sub.5               1 #STR88##                         CH═CH--C.sub.2 H.sub.5     9 C.sub.2 H.sub.5               1 #STR89##                         C.sub.2 H.sub.4 --CH═CH.                                                  sub.2    10 C.sub.2 H.sub.5               1 #STR90##                         CH═CH--CH.sub.2                                                  --C.sub.2 H.sub.5    11 C.sub.2 H.sub.5               2 #STR91##                         C.sub.2 H.sub.5    12 n-C.sub.3 H.sub.7               2 #STR92##                         n-C.sub.3 H.sub.7    13 C.sub.2 H.sub.5               2 #STR93##                         CH═CH.sub.2    14 H.sub.2 C═CH               2 #STR94##                         CH═CH.sub.2    15 H.sub.2 C═CH               2 #STR95##                         n-C.sub.3 H.sub.7    16 C.sub.2 H.sub.5               3 #STR96##                         C.sub.2 H.sub.5    17 n-C.sub.3 H.sub.7               3 #STR97##                         n-C.sub.3 H.sub.7    18 C.sub.2 H.sub.5               3 #STR98##                         CH═CH.sub.2    19 H.sub.2 C═CH               3 #STR99##                         CH═CH.sub.2    20 H.sub.2 C═CH               3 #STR100##                        n-C.sub.3 H.sub.7    21 C.sub.2 H.sub.5               4 #STR101##                        C.sub.2 H.sub.5    22 n-C.sub.3 H.sub.7               4 #STR102##                        n-C.sub.5 H.sub.11    23 C.sub.2 H.sub.5               5 #STR103##                        C.sub.2 H.sub.5    24 n-C.sub.3 H.sub.7               5 #STR104##                        n-C.sub.3 H.sub.7    25 n-C.sub.3 H.sub.7               5 #STR105##                        n-C.sub.5 H.sub.11    26 C.sub.2 H.sub.5               6 #STR106##                        C.sub.2 H.sub.5    27 n-C.sub.3 H.sub.7               6 #STR107##                        n-C.sub.3 H.sub.7    28 n-C.sub.3 H.sub.7               6 #STR108##                        CH═CH.sub.2    29 n-C.sub.3 H.sub.7               7 #STR109##                        n-C.sub.3 H.sub.7    30 n-C.sub.3 H.sub.7               7 #STR110##                        n-C.sub.5 H.sub.11    31 n-C.sub.5 H.sub.11               7 #STR111##                        n-C.sub.3 H.sub.7    32 n-C.sub.3 H.sub.7               8 #STR112##                        n-C.sub.3 H.sub.7               C 97 S.sub.B (97) I; Δε = -4.2; Δn =               +0.025    33 n-C.sub.3 H.sub.7               8 #STR113##                        n-C.sub.5 H.sub.11    34 n-C.sub.5 H.sub.11               8 #STR114##                        n-C.sub.3 H.sub.7    35 n-C.sub.3 H.sub.7               9 #STR115##                        n-C.sub.3 H.sub.7    36 n-C.sub.3 H.sub.7               9 #STR116##                        n-C.sub.5 H.sub.11    37 n-C.sub.5 H.sub.11               9 #STR117##                        n-C.sub.3 H.sub.7    38 n-C.sub.3 H.sub.7               0 #STR118##                        F    39 n-C.sub.5 H.sub.11               1 #STR119##                        CN    40 n-C.sub.3 H.sub.7               2 #STR120##                        OCF.sub.3    41 C.sub.2 H.sub.5               3 #STR121##                        n-C.sub.3 H.sub.7    42 C.sub.2 H.sub.5               4 #STR122##                        n-C.sub.3 H.sub.7    43 n-C.sub.3 H.sub.7               4 #STR123##                        n-C.sub.3 H.sub.7    44 C.sub.2 H.sub.5               5 #STR124##                        n-C.sub.3 H.sub.7    45 n-C.sub.3 H.sub.7               5 #STR125##                        n-C.sub.3 H.sub.7    46 n-C.sub.3 H.sub.7               6 #STR126##                        n-C.sub.3 H.sub.7    47 C.sub.2 H.sub.5               6 #STR127##                        CH═CH.sub.2    48 H.sub.2 C═CH               6 #STR128##                        C.sub.2 H.sub.5    49 H.sub.2 C═CH               6 #STR129##                        CH═CH.sub.2    50 C.sub.2 H.sub.5               7 #STR130##                        n-C.sub.3 H.sub.7    51 C.sub.2 H.sub.5               8 #STR131##                        n-C.sub.3 H.sub.7    52 C.sub.2 H.sub.5               9 #STR132##                        n-C.sub.3 H.sub.7    53 C.sub.2 H.sub.5               0 #STR133##                        n-C.sub.3 H.sub.7    54 C.sub.2 H.sub.5               1 #STR134##                        n-C.sub.3 H.sub.7    55 C.sub.2 H.sub.5               2 #STR135##                        n-C.sub.3 H.sub.7    56 n-C.sub.3 H.sub.7               3 #STR136##                        n-C.sub.3 H.sub.7    57 H.sub.2 C═CH               4 #STR137##                        n-C.sub.3 H.sub.7    58 C.sub.2 H.sub.5               5 #STR138##                        OCF.sub.3    59 n-C.sub.3 H.sub.7               6 #STR139##                        n-C.sub.3 H.sub.7    60 H.sub.2 C═CH               7 #STR140##                        n-C.sub.3 H.sub.7    61 C.sub.2 H.sub.5               8 #STR141##                        OCF.sub.3    62 n-C.sub.3 H.sub.7               9 #STR142##                        n-C.sub.3 H.sub.7    63 H.sub.2 C═CH               0 #STR143##                        n-C.sub.3 H.sub.7    64 C.sub.2 H.sub.5               1 #STR144##                        OCF.sub.3    65 n-C.sub.3 H.sub.7               2 #STR145##                        n-C.sub.3 H.sub.7    66 C.sub.2 H.sub.5               3 #STR146##                        n-C.sub.3 H.sub.7    67 C.sub.2 H.sub.5               4 #STR147##                        C.sub.2 H.sub.5    68 n-C.sub.3 H.sub.7               5 #STR148##                        n-C.sub.3 H.sub.7    69 C.sub.2 H.sub.5               6 #STR149##                        n-C.sub.3 H.sub.7    70 C.sub.2 H.sub.5               7 #STR150##                        C.sub.2 H.sub.5    71 n-C.sub.3 H.sub.7               8 #STR151##                        n-C.sub.3 H.sub.7    72 C.sub.2 H.sub.5               9 #STR152##                        n-C.sub.3 H.sub.7    73 C.sub.2 H.sub.5               0 #STR153##                        C.sub.2 H.sub.5    74 n-C.sub.3 H.sub.7               1 #STR154##                        n-C.sub.3 H.sub.7    75 C.sub.2 H.sub.5               2 #STR155##                        C.sub.2 H.sub.5    76 n-C.sub.3 H.sub.7               3 #STR156##                        n-C.sub.3 H.sub.7               C 109 S.sub.B > 200 decomp.    77 C.sub.2 H.sub.5               4 #STR157##                        n-C.sub.3 H.sub.7    78 C.sub.2 H.sub.5               5 #STR158##                        C.sub.2 H.sub.5    79 n-C.sub.3 H.sub.7               6 #STR159##                        n-C.sub.3 H.sub.7    80 C.sub.2 H.sub.5               7 #STR160##                        n-C.sub.3 H.sub.7    81 C.sub.2 H.sub.5               8 #STR161##                        C.sub.2 H.sub.5    82 n-C.sub.3 H.sub.7               9 #STR162##                        n-C.sub.3 H.sub.7    83 C.sub.2 H.sub.5               0 #STR163##                        n-C.sub.3 H.sub.7    84 C.sub.2 H.sub.5               1 #STR164##                        C.sub.2 H.sub.5    85 n-C.sub.3 H.sub.7               2 #STR165##                        n-C.sub.3 H.sub.7    86 C.sub.2 H.sub.5               3 #STR166##                        F    87 n-C.sub.3 H.sub.7               4 #STR167##                        n-C.sub.3 H.sub.7    88 C.sub.2 H.sub.5               5 #STR168##                        OCF.sub.3    89 n-C.sub.3 H.sub.7               6 #STR169##                        n-C.sub.3 H.sub.7    90 C.sub.2 H.sub.5               7 #STR170##                        CN    91 n-C.sub.3 H.sub.7               8 #STR171##                        CF.sub.3    92 n-C.sub.3 H.sub.7               9 #STR172##                        F    93 n-C.sub.3 H.sub.7               0 #STR173##                        OCF.sub.3    94 n-C.sub.3 H.sub.7               1 #STR174##                        OCF.sub.3    95 n-C.sub.3 H.sub.7               2 #STR175##                        OCF.sub.3    96 n-C.sub.3 H.sub.7               3 #STR176##                        OCF.sub.3    97 n-C.sub.3 H.sub.7               4 #STR177##                        F    __________________________________________________________________________

We claim:
 1. A 1,3-dioxane compound having axial fluorine substitution,of the formula I

    R.sup.1 --(A.sup.1 --Z.sup.1).sub.m --W--(Z.sup.2 --A.sup.2).sub.n --R.sup.2(I)

in which W is ##STR178## where ##STR179## are each, independently of oneanother, ##STR180## n₁, n₂ and n₃ are each, independently of oneanother, 0 or 1,provided that one of the groups ##STR181## must be##STR182## and another of these groups must simultaneously be ##STR183##are each, independently of one another, ##STR184## n₄, n₅ and n₆ areeach, independently of one another, 0or 1, provided that one of thegroups ##STR185## must be ##STR186## R¹ and R² are each, independentlyof one another, an alkyl or alkenyl radical having 1 to 12 carbon atomswhich is unsubstituted, monosubstituted by CN or CF₃ or at leastmonosubstituted by halogen, where one or more CH₂ groups in theseradicals are optionally replaced, independently of one another, by--O--, --S--, --CO--, --CO--O--, --O--CO-- or --O--CO--O-- in such a waythat hetero atoms are not linked directly to one another, R² isalternatively F, Cl or CN; A¹ and A² are each, independently of oneanother,a) a trans-1,4-cyclohexylene radical in which, in addition, oneor more non-adjacent CH₂ groups are optionally replaced by --O-- and/or--S--, b) a 1,4-cyclohexenylene radical, c) a 1,4-phenylene radical, inwhich, in addition, one or two CH groups may be replaced by N, or d) aradical selected from the group consisting of 1,4-bicyclo2.2.2!octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl and1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals a), b) and c)are optionally substituted by CN or F; Z¹, Z², Z³ and Z⁴ are each,independently of one another,--CO--O--, --O--CO--, --CH₂ O--, --OCH₂ --,--CH₂ CH₂ --, --CH═CH--, --C.tbd.C-- or a single bond; and m and n areeach, independently of one another,
 0. 1, 2 or 3;provided that n₁ +n₂+n₃ +m+n=2, 3 or 4, and n₄ +n₅ +n₆ +m+n=1, 2, 3 or
 4. 2. A 1,3-dioxanecompound of the formula I according to claim 1, wherein n₁ +n₂ +n₃+m+n=2 or 3, and n₄ +n₅ +n₆ +m+n=2 or
 3. 3. A 1,3-dioxane compound ofthe formula I according to claim 1, wherein R¹ and R² are each,independently of one another, unsubstituted, straight-chain alkyl or 1E-or 3E- alkenyl having 1 to 12 carbon atoms.
 4. A 1,3-dioxane compound ofthe formula I according to claim 1, wherein Z¹ and Z² are single bonds,and Z³ and Z⁴ are either single bonds or --CH₂ CH₂ -- groups.
 5. A1,3-dioxane compound of claim 1 of the formula ##STR187##
 6. A1,3-dioxane compound of claim 1 of the formula in whichone of theradicals L^(1*) and L^(2*) is F and the other is H or F.
 7. A1,3-dioxane compound of claim 1 of the formula ##STR188## in which y is1 or
 2. 8. A liquid-crystalline medium which comprises at least one1,3-dioxane compound according to claim
 1. 9. A liquid-crystallinemedium having at least two liquid-crystalline components, wherein atleast one component is a 1,3-dioxane compound of the formula I accordingto claim
 1. 10. A liquid-crystal display element, which comprises aliquid-crystalline medium according to claim
 9. 11. An electro-opticaldisplay element, which comprises as dielectric, a liquid-crystallinemedium according to claim
 9. 12. A TFT or STN liquid-crystal displaycontaining a liquid-crystal display element according to claim 10.